Glycerides, C16-18

Bioaccumulation: aquatic / sediment

Key value for chemical safety assessment

BCF (aquatic species):

285.92 L/kg ww

Additional information

The BCF value of ‘Glycerides, C16-18’ was estimated through the computation methods recommended in Chapter R.7a, in: Guidance on information requirements and chemical safety assessment. Since the Kow values for some of the constituents were >10, the calculations were performed using more than one QSAR programs such as BCFBAF v3.01 of EPIWEB v 4.1, BCF (CAESAR) 2.1.14 and T.E.S.T US EPA model v.4.1 as stated in table R.7.10-3 of the REACH guidance document and/or the ECHA practical guide 5. As the test substance is a UVCB/mixture of different constituents (i.e. glycerides of fatty acids and free fatty acids) theBCF values were determined for representative substances of each class present >10% to represent the lower and upperlimit of the test substance. Hence, the BCF estimations were carried out for palmitic acid and stearic acid representing free fatty acids, glyceryl palmitate and glyceryl stearate representing monoglycerides, disteatin and dipalmitin representing diglycerides, tripalmitin and tristearin representing triglycerides of fatty acids.SMILES notations were used as the input parameters for the programs/softwares. The BCF values estimated using BCFBAF v.3.02 for the representative constituents ranged between 112.15 -498.70 L/kg for fatty acids, 2.03 L/kg for the triglycerides, 68.41 - 246.57 L/kg for monoglycerides and 2.03 -7.20 L/kg for diglycerides substance class. Except for the Kow values of di and triglycerides, the estimation by this method is more or less accurate as the molecular weight and the Kow range for the different constituents of test substance were determined to be within the molecular weight and Kow range of the training set compounds. Hence, considering this and the fact that all the representative constituent classes are hydrophobic with Kow 6, they were additionally modelled using the BCF (CAESAR) 2.1.14 model. This model is based on Dimitrov et al., 2005 experimental database, which is recognised to cover hydrophobic compounds. The BCF values estimated using Caesar BCF model for the representative constituents were estimated to range between 58 -330L/kg for fatty acids, 0.84 -0.95 L/kg for the triglycerides, 9 -11 L/kg for monoglycerides and 2 L/kg for diglycerides substance class.However, these estimations using BCF (CAESAR) were reported to be not veryreliable. Therefore, to further, increase the confidence of the predictions, the BCF values were additionally estimated using the BCF interface of the US EPA T.E.S.T QSAR model. This model uses several methodologies (such as hierarchical clustering, single model, group contribution, FDA, nearest neighbour) to predict an overall average BCF value under the name ‘consensus method’. The respective average BCF ranges for the representative constituents were estimated to be 12.29 -29.05L/kg for fatty acids, 3.7 -3.99 L/kg for the triglycerides, 13.46 -25.29 L/kg for monoglycerides and 7.5 -9.11 L/kg for diglycerides substance class.However, the different training set substances used for the BCF estimation for the representative substances via the US EPA TEST program were not very similar and had presence of other functional groups. Overall, considering that the estimated values from the three models lie more or less in the same BCF range, anaverage estimated BCF value was determined to reduce the overall uncertainty or limitations of each of the models. Therefore, based on the BCF estimations for the representative constituents, the estimated BCF value of the ‘Glycerides , C16-18’ can be considered to range between 2.19 -285.92 L/kg (US EPA, 2021; Zhao et al., 2008). This is in line with the statement stated in chapter R.11 from ECHA i.e., "the aquatic BCF of a substance is probably lower than 2000 if the calculated Log Kow is higher than 10".